Known processes for producing hydrogen cyanide from methane and ammonia include the oxidative Andrussow process and the non-oxidative methane-ammonia (Degussa/BMA) and Shawinigan processes. The Andrussow process uses either a Pt—Rh or Pt—Ir gauze catalyst; the methane-ammonia (BMA) process uses a Pt gauze catalyst. Both processes require high temperatures: the Andrussow process requires a temperature greater than 1000° C. and the methane-ammonia (BMA) process requires a temperature greater than 1200° C. The Shawinigan process does not use a catalyst and requires the temperature of the process to be kept at greater than 1500° C. Ullmann's Encyclopedia of Industrial Chemistry, Cyano Compounds, Inorganic, 2012, p. 676.
The high temperatures required for the known processes are due to the endothermic nature of the process. However, the competing side reaction of the decomposition of ammonia to nitrogen and hydrogen is also thermodynamically favored at higher temperatures. Angew. Chem. Int. Ed. (2011), 50, 4601-4605.
In order to reduce production costs and competing side reactions, it is an advantage to lower the temperature required for reaction processes. In order to lower the temperature of the process, an exothermic oxidative process such as the Andrussow process may be chosen over an endothermic non-oxidative process. However, the Andrussow process still requires temperatures of greater than 1000° C. and is less safe to operate than the endothermic non-oxidative processes. A safer process is preferable.
An additional advantage in order to reduce production costs would be to lower the cost of the materials used. It is desirable to use alternative, cheaper catalyst metals such as base metals, e.g. Fe, Co, Ni, rather than noble metals such as Pt.
With regard to investigating the use of alternative catalyst metals, Angew. Chem. Int. Ed. (2011), 50, 4601-4605 provides a descriptor-based understanding of trends in activity and selectivity of various catalyst metals with respect to the preparation of hydrogen cyanide from methane and ammonia. The information analyzed is the result of modelling the adsorption energies of carbon and nitrogen on transition-metal surfaces. It should be noted that the results analyzed are theoretical models rather than practical examples.
The article is directed towards Pt catalysts and it is suggested that cobalt (Co), among other metals, would be an active metal towards ammonia adsorption at a temperature of 1100° C. Ammonia adsorption is a precursor step to both hydrogen cyanide production and the competing side reaction of nitrogen production. The theoretical reaction conditions indicate that a catalyst comprising Co would produce significant amounts of nitrogen and would therefore not be selective for hydrogen cyanide production.
Therefore, it is also desirable to provide a process that employs a cheaper catalyst metal and that is selective for the production of hydrogen cyanide.
The described prior art provides processes for the production of hydrogen cyanide from methane and ammonia with gauze catalysts comprising Pt and at temperatures above 1000° C. The present invention provides catalysts comprising a cheaper metal, i.e. Fe, Co or Ni, wherein the catalyst is selective for the production of hydrogen cyanide and is preferably performed at temperatures of less than 1000° C.
The catalysts of the present invention provide additional advantages such as the ability to use cheaper forms of catalysts such as pellets and extrudates.